WO2001084642A1

WO2001084642A1 - Piezo-ceramic multilayer component for measuring instruments and method for the production thereof

Info

Publication number: WO2001084642A1
Application number: PCT/EP2000/007506
Authority: WO
Inventors: Sergej Lopatin; Igor Getman; Anatoliy Panitch; Yuriy Wusewker
Original assignee: Endress + Hauser Gmbh + Co. Kg
Priority date: 2000-04-27
Filing date: 2000-08-03
Publication date: 2001-11-08
Also published as: AU2000269919A1; US6710517B2; CN1330014C; ATE540433T1; CN1452792A; EP1277243A1; US20040095041A1; US6834419B2; JP2003533032A; RU2264678C2; US20020011589A1; EP1277243B1

Abstract

The invention relates to an electromechanical drive or a sensor element comprised of stacked piezoelectric elements. The drive or sensor element is provided for measuring instruments and also operates at very high temperatures. To this end, the novel drive or sensor element (10) comprises several piezoelectric ceramic layers (12a - f), whereby each electrode layer (16a - e) is arranged between the two facing surfaces of each set of directly adjacent piezoelectric ceramic layers. Wire-shaped connectors (18 a - b), which are provided for electrically contacting the electrode layers (16a - e) and which lead out of said electrode layers (16a - e), extend inside grooves (14a - d) located in the electrode layers (16a - e).

Description

PIEZOCERAMIC MULTILAYER COMPONENT FOR MEASURING DEVICES AND THEIR PRODUCTION METHOD

The invention relates to an electromechanical drive or a 5 sensor element for a measuring device and a method for their production. It relates in particular to drives and sensor elements made of piezoelectric elements and the measuring devices equipped with them in a stacked construction.

10 Known measuring devices of this type are e.g. piezoelectric acceleration sensors and level measuring devices. These measuring devices usually comprise a base body on which the drive or the sensor element is attached, these being piezoelectric elements, electrodes and electrical connectors and

15 connections included. The piezoelectric elements are electrically connected to one another and connected to an electronic circuit corresponding to the application.

Piezoelectric measuring devices of this type show a relatively large charge sensitivity and a relatively low transverse sensitivity. However, their particular disadvantage is their relatively limited, effective working range at high temperatures from e.g. 200 ° C, under the influence of high static pressures up to e.g. 500 bar or, in the case of the acceleration sensors, at high dynamic loads where accelerations of up to 2000 g occur.

The sensitivity of the piezoelectric measuring devices to the described loads is due to the structure of their drive or sensor element. Such a drive or 30 is usually such a sensor element made of successive and geometrically coordinated piezo-electric Elements, electrodes as well as electrical connectors and connections. Different materials, such as piezoceramic and metal, are combined with one another, which differ in their elasticity modules and their respective coefficients of thermal expansion. Under the influence of the aforementioned high temperatures and / or large static and dynamic loads on the sensor element or the drive, extensive mechanical planar voltages arise in the piezoelectric elements themselves, which not only reduce the strength of the sensor element but also the useful or measurement signal ,

In known measuring devices of the type described, a monolithic thin-film capacitor constructed in a layered construction has also proven to be advantageous, which also, e.g. in level gauges, can be constructed as a multiple capacitor from thin layers. The layer sequence of the monolith comprises the piezoelectric thin layers and electrodes, electrical connectors arranged along the monolith being provided. Usually, a connector (often referred to as a "rail") then connects the electrodes of one pole and another connector connects those of the other pole. Such a monolithic structure has great stability and strength and allows vibration parameters to be measured very precisely by lowering the relative coefficient of the transverse transformation.

However, this structure is based on an asymmetrical shape of the electrodes, which has on one side a projecting part for connection to a rail and on the opposite side an insulating play to the other rail. Inhomogeneities in the structural design of such drives or sensor elements act however negatively affects the size of the relative coefficient of the transverse transformation. In addition, the asymmetrical shape of the electrodes does not allow the entire electrode area of the piezoelectric layers to be charged, as would be desirable to increase the coefficient of the transverse transformation. The smaller the metallization area of the piezoelectric layer under consideration in relation to its actual usable area, the more the coefficient of transformation is reduced.

The invention is therefore based on the object of specifying piezo-electric drives or sensor elements and a method for their production which allow measuring instruments equipped therewith, avoid the disadvantages described above and which can also be influenced by high temperatures or high static and Distinguish dynamic loads with great measuring accuracy.

This object is achieved by a first variant of the invention by means of an electromechanical drive or a sensor element in a layered construction, the or that

- from several piezoelectric ceramic layers,

- An electrode layer arranged between two mutually facing surfaces of directly adjacent piezoelectric ceramic layers and

an electrical connector for making electrical contact with the electrode layer,

- The connector is also arranged between the two facing surfaces of the piezoelectric ceramic layers and led out. This object is also achieved by a second variant of the invention by means of an electromechanical drive or a sensor element in a layered construction,

with a plurality of piezoelectric ceramic layers, in which the mutually facing surfaces of directly adjacent piezoelectric ceramic layers are metallized by applying a metal coating, which are joined together by means of diffusion welding,

- so that an electrode layer is formed by the metallized surfaces,

- Which can be contacted via an electrical connector.

In a preferred embodiment of the invention it is provided that in at least one of the two mutually facing surfaces of the piezoelectric ceramic layers a groove is provided which at least partially receives the electrical connector.

In another preferred embodiment of the invention, the connector is a wire extending beyond the surfaces of the piezoelectric ceramic layers.

In yet another preferred embodiment of the drive or sensor element according to the invention, at least three piezoelectric ceramic layers and at least two grooves are provided, these grooves being arranged offset with respect to one another and with respect to a longitudinal axis of the drive or sensor element. In a development of a preferred embodiment of the invention, the wire has a wavy or serrated structure.

In other developments of the invention, the piezoelectric ceramic layers consist of PZT material, such as, for example, PbMg ₀₃₀₈ Nb ₀₆₁₇ Ti ₀₀₇₅ O ₃ , or ceramic _layers made of a material with a Curie temperature greater than 400 ° C., for example Na ₀₅ Bi ₄₅ Ti ₄ O ₁₅ or Bi ₃ TiNb0 ₉ ..

In other developments of the invention

Electrode layers made of a metallic material with a Curie temperature greater than 400 ° C, e.g. made of bismuth titanate.

Still further developments of the invention relate to wires made of a metallic material with a high temperature stability greater than 250 ° C. and those made of a silver-containing, stainless steel-containing material or a material that contains a nickel alloy.

The mentioned object on which the invention is based is also achieved by an electromechanical drive or a

Solved sensor element in a layered construction, which is produced by a method which comprises the following steps:

- Manufacture of ceramic layers from electroactive material according to a method common in ceramic technology with desired dimensions and with a reserve of 2-3 mm for each dimension, taking into account the subsequent mechanical processing; - Grinding the ceramic layers to a predetermined thickness of for example 0.15 to 03 mm is reached;

- Cutting a groove in a side of the ceramic layers to be metallized;

- The depth of the groove must not be deeper than half the thickness of the ceramic layer under consideration;

- Metal coating at least this side of the ceramic layers by twice applying a silver-containing paste and subsequent annealing at a temperature of 800-820 ° C;

- gluing the metallized surfaces of two ceramic layers with a cellulose glue;

- Diffusion welding of the glued layers by annealing on a

Temperature of 780-800 ° C and uniaxial compression under one

Pressure of 3-5 kg / cm ² in the course of 3 hours and cooling to room temperature;

- pulling a connector wire into a groove;

- Action of an electric field on the wires under high temperature and establishment of the desired polarity of the electrode layers

Connecting the same poles of the drive or the sensor element;

- Checking the desired parameters and piezo-electric properties of the drive or the sensor element.

A fill level limit switch is also created, which has a drive and a sensor element according to the invention is equipped, in a further development of such a level limit switch the sensor element is separated from the drive by a non-polarized ceramic layer.

In addition, an acceleration sensor with a sensor element according to the invention is created.

The particular advantage is that the construction according to the invention and the manufacturing method according to the invention make it possible to create a piezoelectric drive or a sensor element in which the coefficient of charge transformation and the measuring accuracy of the sensor element are improved in that the relative coefficient of the transverse Transformation in a wide temperature range and with high static and dynamic loads is reduced.

The invention is explained and described in detail below using several exemplary embodiments and with reference to a drawing. Show:

Figure 1 is a perspective view of a multi-layer previously known piezoelectric drive or sensor element.

Fig. 2 is a perspective view of a first

Embodiment of a multilayer piezoelectric drive or sensor element according to the invention; Fig. 3 is a schematic side view of an expanded

Drive or sensor element according to Fig. 2;

Fig. 4 is a schematic representation of several layers of a second embodiment of a piezoelectric

Drive or sensor element according to the invention;

Fig. 5 schematic side views of two specially shaped

Wires for a drive or a sensor element according to the

Invention;

6 shows a sectional illustration of an acceleration sensor with a multilayer piezoelectric sensor element according to the invention; and

Fig. 7 is a schematic, partially cut open

Representation of a level switch with a piezo-electric

Drive and a piezoelectric sensor element according to the

Invention.

To the essential differences of the invention from the prior art

To be able to demonstrate technology is a previously known piezoelectric Electric drive or a previously known piezoelectric sensor element 1 is shown. This is referred to below and for the sake of simplicity as piezoelectric element 1. It essentially consists of piezo-ceramic disks 2a, b, c, d in which at least one of the surfaces facing one another is metallized and which are arranged one above the other with the interposition of electrodes 3a, b, c and are joined together in the usual manner and in this way that a structure of a monolithic film capacitor is achieved. 1 also shows a metallic strip-shaped connector 4, which is fitted on the outside of the outer surface of the piezoelectric element 1 and which electrically connects the electrodes 3a and 3c to one another at two connection points 5a and 5b. Another connector of the same type is usually mounted on the other side of the lateral surface of the piezoelectric element 1, which in turn is electrically connected to the electrode 3b, but cannot be seen in FIG. 1 due to the selected type of illustration. Electrical connecting conductors (not shown here) can usually be connected to both connectors to form a drive or evaluation electronics (also not shown here for the sake of simplicity).

In order to prevent the strip-shaped connector 4 from making undesired contact with the electrode 3b, it must be recessed at the point where the connector 4 is provided and virtually spring back into the interior of the piezoelectric element 1. It cannot cover the entire available surface of the disk 2b (or 2c), which, as mentioned at the beginning, has a negative influence on the transformation coefficient at this point of the piezoelectric element 1. The same applies to the connector (not visible here) and the electrode 3a. You too must maintain proper decency towards the connector in order to avoid undesired contacting.

Another disadvantage of the piezoelectric element 1 known in FIG. 1 has also already been mentioned at the beginning. Flat or strip-shaped metallic connectors, such as connector 4, exhibit an expansion behavior at higher temperatures, which differs remarkably from that of ceramic disks 2a-d. This thermally induced effect can go so far that the connection points 5a, b can be destroyed, as a result of which the entire function of the piezoelectric element 1 is questioned.

A piezoelectric drive or a sensor element 10 shown in FIG. 2, which is a first and preferred, is more advantageous

Embodiment of the invention is. In this example, the piezoelectric element 10 constructed to form a monolithic layer capacitor comprises four piezo-ceramic disks 12a, 12b. 12c, 12d, into which grooves 14a and 14b as well as grooves 14c and 14d arranged offset by approximately 180 ° are cut. As will be explained later, the grooves 14a-d are cut into the finished ceramic disks 12a-d. The surface of each of the ceramic disks 12a-d, which contains the groove 14a-d, is metallized together with the entire surface, as illustrated by the example of the layer designated 16a. After the ceramic disks I2a-d have been joined together in the manner shown in FIG. 2 and preferably by diffusion welding, full-area electrode layers 16a, 16b become through the metallized layers. 16c, 16d. The electrode layers 16a and 16c are conductively connected to one another by a wire drawn into the grooves 14a and 14b as a connector 18a. It is possible in a simple manner to prevent undesired contacting with other electrode layers by slightly projecting the connector beyond the lateral surface of the piezoelectric element 10. A wire-shaped connector 18b connecting the electrode layers 16b and 16d, which was drawn into the grooves 14c and 14d similarly to the connector 18a, is indicated in FIG. 2. A further electrical connecting line to a drive or measuring electronics can be connected in a simple manner to the connectors.

Of course, it is not absolutely necessary for the invention to arrange the connectors 18a and 18b in the sense of the loops shown by way of example in FIG. 2. It is equally possible to have the wire-shaped connectors as individual sections, i.e. in the sense of individual wires through the grooves and only then connect the individual wires in the desired manner. In principle, each individual electrode can be controlled individually if desired. The wire-shaped connectors 18a and 18b ensure a permanent connection to the electrodes even at high temperatures and enable a full-surface electrode layer.

For reasons of strength, it is advisable not to cut the grooves deeper into the ceramic layers than half the thickness of the respective ceramic disk illustrated by "S" in FIG. 2. In practice, a groove depth that is approximately 0.3 times the thickness of the ceramic disk in question has proven to be particularly advantageous. Ceramic disks are preferably made from PZT material. The suitability of the piezoelectric element 20 according to the invention is further improved if the ceramic disks are made of PbMg ₀₃₀₈ Nb ₀₆₁₇ Ti ₀₀₇₅ O ₃ . A particularly high temperature suitability is obtained if the piezoelectric ceramic disks are made of a material with a Curie temperature greater than 400 ° C, for example Na ₀₅ Bi ₄₅ Ti ₄ O ₁₅ or Bi ₃ TiNbO ₉ .

The properties of the materials used for the electrode layers and for the wire-shaped connectors should be matched to those used for the ceramic disks. For example, it is recommended to use a metallic material with a Curie temperature greater than 400 ° C for the electrode layers, preferably material made from bismuth titanate. In the case of the wire-shaped connectors, those made of a material with a high temperature stability greater than 250 ° C. have proven to be particularly advantageous, wires made of a silver-containing, stainless steel-containing material or one that should be given preference to a nickel alloy.

In order to illustrate the various possibilities and designs which result with a piezoelectric element 10 according to the invention, FIG. 3 shows an expanded piezoelectric element 10 with now six compared to the one that is "upside down" in FIG. 2 Ceramic disks 12a, 12b, 12c, 12d, 12e, 12f, five grooves 14a, 14b, 14c, 14d, 14e and, accordingly, five electrode layers 16b, 16c, 16d, 16e, 16f are shown. In continuation of the construction shown in FIG. 2, the wire-shaped connector 18a does not only run in the grooves 14a, 14b and 14e and therefore connects the electrode layers 16a, 16c, 16e to the same polarity as the wire-shaped connector 18b does with the electrode layers 16b and 16d. Otherwise, what was said above about the piezoelectric element 10 shown in FIG. 2 applies here in the same way.

4 shows a second and preferred embodiment of a piezoelectric drive or sensor element according to the invention. This sensor element or drive, which is called the piezoelectric element 20 for the sake of simplicity, is shown in such a way that the course of the grooves 24a, 24b, 24c, 24d, cut therein is illustrated in the ceramic disks 22a, 22b, 22c, 22d shown spaced apart from one another , In contrast to the grooves 14a-e shown in FIGS. 2 and 3, the grooves 24a-d do not run through the center of the ceramic disks 22a-d. The grooves 24a-d do not intersect a longitudinal axis 29 shown in FIG. 4 but run in the general sense of a secant in relation to the circular surfaces of the ceramic disks 22a-d shown here by way of example.

The position of the grooves 24a-d is arbitrary per se, but they should, in turn, be offset from one ceramic disk to the other, similarly to the grooves 14a-d in FIG. 2, and preferably such that an overlap of in the grooves 24a and 24c or 24b and 24d arranged connectors 28a or 28b can be excluded. The distance of the grooves 22a-d from the edge of the ceramic disks 22a-d is to be aligned according to the requirements placed on the mechanical strength of the ceramic disks 22a-d. It has been shown that the grooves are preferably arranged halfway between the longitudinal axis 29 and the edge of the respective ceramic disk. The metallized surfaces from which the electrode layers are formed by joining the ceramic disks 22a-d (see also FIGS. 2 and 3) are designated in FIG. 4 by "26a, 26b, 26c, 26d". For the rest, what has already been said about the embodiments of the invention shown in FIGS. 2 and 3 applies.

5 shows, by way of example, two different designs of the wire-shaped connectors 18a, b and 28a, b (see FIGS. 2 to 4), which have proven to be particularly advantageous in practice. that one and one serrated connector 32b are advantageous. A wave-shaped connector 32a as shown in FIG. 5, as well as a jagged connector 32b, enables a reliable electrical contacting of the electrode layers through its "wave crests" or through its jags, without the respective elastic properties being reduced in the case of the materials mentioned above. It is clear that the corrugation or serration of the wire-shaped connections 32a, b is to be selected so that their threading into the grooves 14a-d or 24a-d (see FIGS. 2 to 4) is not hindered.

The electromechanical drives or sensor elements according to the invention shown in FIGS. 2 to 4 are manufactured as follows. The method is explained using the example of the piezoelectric element 10 shown in FIG. 2. Without restricting the invention, the method can also be used for all other possible electromechanical drives or sensor elements according to the invention.

First, the ceramic disks 12a-d are made from an electroactive material described above by a method customary in ceramic technology

Dimensions made, with a reserve of 2-3 mm for each Dimension is provided taking into account the subsequent mechanical processing. The ceramic disks 12a-d are then ground until a predetermined thickness S of, for example, 0.15 to 03 mm is reached. After the desired groove 14a-d has been cut into each surface of a ceramic disk 12a-d to be metallized, the groove not being allowed to be deeper than half the thickness S of the ceramic layer under consideration, the surface in question, including the groove, is coated with a metal. This is achieved by applying a silver-containing paste at least twice and then tempering at a temperature of 800-820 ° C. The ceramic disks are then connected to one another in the desired manner and depending on the desired alignment of the grooves, two ceramic layers being glued to one another by gluing with cellulose glue. The glued ceramic disks are then used in a suitable frame and baked together by diffusion welding at a temperature of 780-800 ° C. and uniaxial compression under a pressure of 3-5 kg / cm ² over a period of 3 hours to form a monolithic structure and then until cooled to room temperature. One connector wire each is drawn into a groove, the electrode layers formed by the metallized layers being polarized in the desired manner by the action of an electric field on the connector wires at high temperature. The electrode layers are then interconnected in the desired manner. The desired parameters and the piezoelectric properties of the drive or sensor element are then checked.

For the sake of completeness, an acceleration sensor 40 is shown in FIG. 6, which, according to FIG Invention is equipped. The sensor element 42 comprises plate-shaped, ie angular ceramic layers 41a, 41b, 41c,

41 d, 41 e, 41 f and electrode layers arranged between them, which together form a monolithic multilayer capacitor already mentioned above. The sensor element

42 is fastened on a base plate 46 by means of a fastening rod 44. For this purpose, the individual ceramic plates 41a-f have central openings similar to those of the ceramic disks 22a-d in FIG. 4, which together form a central, axial passage of the sensor element 42. The fastening rod 44 is fixedly connected to the base plate 46, runs through the central, axial passage of the sensor element 42 and also extends into a section which is provided with a thread 48. The sensor element 40 is therefore placed over the fastening rod 44 and is fastened by means of a retaining nut 50 which is screwed onto the fastening rod 44 and mechanically connected to the base plate 46. Two insulation layers 54a, 54b serve for the electrical insulation of the sensor element 40 from the base plate 46 and a cover 52 forming a housing.

The sensor element 40 is constructed essentially in a similar manner to the piezoelectric elements 10 and 20 shown in FIGS. 2 to 4. In contrast to this, however, there are grooves 56a, 56b, 56c, 56d, 56e, 56f for receiving wire-shaped ones Connectors 58a, 58b are provided, which grooves run on the outer edges, so to speak on the edges of the ceramic plates 41a-f. The wire-shaped connectors 58a, b connecting the electrodes of the same polarity in the desired manner run into electrical connecting lines 60a, 60b, which are combined in a cable 62, which in turn is connected to measuring electronics, not shown here. 7 shows an example of a further measuring device, a level measuring device, more precisely: a level limit switch 70, which is equipped with a piezoelectric element 72, which is constructed as a monolithic block both from a drive and from a sensor element according to the invention. The fill level limit switch 70 comprises a housing 74 and two oscillating rods 76a, 76b attached to it. The functions of such level limit switches with tuning fork-like vibrating rods are generally known and are therefore not explained further here.

The piezoelectric element 72 is fastened in the interior of the housing 74 by means of a fastening element 78. The housing also accommodates drive and measuring electronics 80, shown schematically here.

In principle, the piezo-electric element 72 is again made up of piezo-ceramic disks 82a, 82b, 82c, 82d, 82e, 82f and electrode layers (not shown here), similar to the piezo-electric element according to FIG. 3. The difference here is that a sensor element is formed with ceramic disks 82a, 82b and 82c and a drive with ceramic disks 82e and 82f. In order to avoid undesirable voltage effects from the drive element on the sensor element, a non-metallized ceramic disk 82d is provided in between.

The piezoelectric element 72 also has two terminating elements 84a, 84b, with which it bears on the one hand on a part of the housing 74 forming a membrane 86 and on the other hand on the fastening element 78. LIST OF REFERENCE NUMBERS

1 previously known drive or sensor element

2a-d piezo-ceramic disc

3a-c electrodes

4 connectors

5a, b connection points

10 first variant of the invention. Drive or

sensor element

12a-f piezo-ceramic disc

14a-d grooves

16a-e electrode layer

18a, b wire-shaped connector

19a, b connecting line to the measuring or drive electronics

20 second variant of the invention. Drive or

sensor element

22a-d piezo-ceramic disc

24a-d grooves

26a-d electrode layer

28a, b wire-shaped connector

29 longitudinal axis of (20)

32a corrugated wire

32b jagged wire

40 acceleration sensor

41 a-f ceramic plate

42 piezo-electric sensor element made of square plates

44 fastening rod

46 base plate

48 thread on (44)

50 holding nut

52 cover a, b insulation layer af grooves a, b connector a, b electrical connection cable level switch piezo-electric element housing a, b oscillating rod fastening element drive or evaluation electronics af ceramic layers a, b sealing element of (76) membrane

Claims

claims

1. Electromechanical drive or sensor element in layered construction, the or that

- from several piezoelectric ceramic layers (12a-f; 22a-d; 41 a-f),

- An electrode layer (16a-e; 26a-d) and arranged between two mutually facing surfaces of directly adjacent piezoelectric ceramic layers

an electrical connector (18a, b; 28a, b; 58a, b) for electrically contacting the electrode layer (16a-e; 26a-d),

- The connector (18a, b; 28a, b; 58a, b) also between the two facing surfaces of the piezoelectric

Ceramic layers (12a-f; 22a-d; 41 a-f) is arranged and led out.

2. Electromechanical drive or sensor element in a layered construction,

- With several piezoelectric ceramic layers (12a-f; 22a-d; 41 a-f),

- In the mutually facing surfaces of directly adjacent piezoelectric ceramic layers (12a-f; 22a-d; 41 a-f) by applying a

Metal coating can be metallized,

- which are joined by means of diffusion welding,

- So that an electrode layer through the metallized surfaces

(16a-e; 26a-d) is formed, - Which can be contacted via an electrical connector (18a, b; 28a, b; 58a, b).

3. Drive or sensor element according to one of claims 1 or 2, in which in at least one of the two mutually facing surfaces of the piezoelectric ceramic layers (12a-f; 22a-d; 41a-f) a groove (14a-d; 24a -d; 56a-f) is provided which at least partially accommodates the electrical connector (18a, b; 28a, b; 58a, b).

4. Drive or sensor element according to claim 3, wherein the connector (18a, b; 28a, b; 58a, b) over the surfaces of the piezoelectric ceramic layers (12a-f; 22a-d; 41a-f) extending wire is.

5. Drive or sensor element according to one of claims 3 or 4 with at least three piezoelectric ceramic layers (12a-f; 22a-d; 41a-f) and at least two grooves (14a-d; 24a-d; 56a-f) , in which these grooves (14a-d; 24a-d; 56a-f) are arranged offset to one another and with respect to a longitudinal axis (29) of the drive or sensor element.

6. Drive or sensor element according to one of claims 4 or 5 with a wire-shaped connector (18a, b; 28a, b; 58a, b), the one

Wire with a wavy or serrated structure.

7. Drive or sensor element according to one of claims 1 to 6 with piezoelectric ceramic layers (12a-f; 22a-d; 41a-f) made of PZT material.

8. Drive or sensor element according to one of claims 1 to 7 with piezoelectric ceramic layers (12a-f; 22a-d; 41 af) made of PbMg ₀₃₀₈ Nb ₀₆₁₇ Ti ₀₀₇₅ O ₃ .

9. Drive or sensor element according to one of claims 1 to 8 with piezoelectric ceramic layers (12a-f; 22a-d; 41a-f) made of a material with a Curie temperature greater than 400 ° C, for example Na ₀₅ Bi ₄₅ Ti ₄ O ₁₅ or Bi ₃ TiNb0 ₉ .

10. Drive or sensor element according to one of claims 1 to 9 with electrode layers (16a-e; 26a-d) made of a metallic material with a Curie temperature greater than 400 ° C.

11. Drive or sensor element according to one of claims 1 to 10 with electrode layers (16a-e; 26a-d) made of bismuth titanate.

12. Drive or sensor element according to one of claims 4 to 11 with wire-shaped connectors (18a, b; 28a, b; 58a, b) made of a metallic material with a high temperature stability greater than 250 ° C.

13. Drive or sensor element according to one of claims 4 to 11 with wire-shaped connectors (18a, b; 28a, b; 58a, b) made of a silver-containing, stainless steel-containing material or one containing a nickel alloy.

14. A method for producing an electromechanical drive or sensor element in a layered construction, which comprises the following steps: - producing ceramic layers (12a-f; 22a-d; 41a-f) from electroactive material according to a customary in ceramic technology Process with the desired dimensions and with a reserve of 2-3 mm for each dimension, taking into account the subsequent mechanical processing; - Grinding the ceramic layers (12a-f; 22a-d; 41 af) until a predetermined thickness of, for example, 0.15 to 03 mm is reached;

- Cutting a groove (14a-d; 24a-d; 56a-f) in one side of the ceramic layers (12a-f; 22a-d; 41 a-f) to be metallized;

- The depth of the groove (14a-d; 24a-d; 56a-f) not deeper than half the

Thickness of the ceramic layer under consideration (12a-f; 22a-d; 41 a-f); - metal coating at least this side of the ceramic layers (12a-f;

22a-d; 41 a-f) by twice applying a silver-containing paste and subsequent annealing at a temperature of 800-820 ° C; - Gluing the metallized surfaces of two ceramic layers (12a-f;

22a-d; 41a-f) with cellulose glue;

- Diffusion welding of the glued layers by annealing to a temperature of 780-800 ° C and uniaxial compression under one

Pressure of 3-5 kg / cm ² in the course of 3 hours and cooling to room temperature; - Pulling a connector wire (18a, b; 28a, b; 58a, b) into a groove (14a-d; 24a-d; 56a-f);

- Polarization of the drive or the sensor element by the action of an electric field on the wires (18a, b; 28a, b; 58a, b) at high temperature;

- Connecting the same poles of the drive or the sensor element;

15 level switch (70) with a drive and a sensor element according to one of claims 1 to 14.

16. Level switch (70) according to claim 15, wherein the sensor element is separated from the drive by a non-polarized ceramic layer (82d).

17. Acceleration sensor (40) with a sensor element according to one of claims 1 to 14.